1. Field of the Invention
The present invention relates to a stator of a motor, and more particularly, to a motor stator assembly and a fabrication method thereof for fabricating a yoke by laminating a plurality of steel sheets and fabricating a pole by a powder metallurgy method.
2. Description of the Related Art
Generally, most of electric appliances use a motor as a driving source. The motor comprises a stator assembly for winding and fixing coil, and a mover assembly positioned inside or outside of the stator assembly and rotated by induction magnetic field for transmitting a driving force.
FIG. 1 is a perspective view showing a stator assembly manufactured by a lamination method in accordance with the conventional art.
As shown, the stator assembly comprises: a stator core 1 formed by laminating a plurality of sheets C which are fabricated by blanking steel with a predetermined shape; an insulator 2 installed in the stator core 1; and a coil 3 wound outside of the insulator 2 for forming induction current.
As shown in FIG. 2, the sheets C constituting the stator core 1 includes a yoke 1a formed as a quadrangle shape for forming a magnetic path; and a pole 1b formed integrally with the yoke 1a as a circular arc shape at both sides of an inner circumference surface of the yoke 1a, on which the coil 3 is wound.
The insulator 2 is attached to a part where the yoke 1a and the pole 1b are connected to each other, and is formed with insulating material such as plastic or rubber for insulating between the coil 3 and the stator core 1.
However, in the stator assembly of a lamination method, an amount of scrap loss which is discarded at the time of blanking for fabricating the stator core is more than 35%, and accordingly, loss of material is generated.
Also, since a protector manufactured by injection molding, is inserted between the stator core and the coil, a radius of a part where coil is wound increases, which result in cost rise, a winding resistance is increased, and thus a motor efficiency is decreased.
To solve the above problems, as shown in FIGS. 3 and 4, the stator assembly of powder metallurgy method comprises: a frame 5 formed by inputting magnetic powder material into a mold of a predetermined shape, applying a predetermined pressure, and heating with a predetermined temperature; and a coil 6 wound on a winding groove 5c of the frame 5 for generating induction magnetism.
The frame 5 includes a yoke 5a formed as a closed curve of a quadrangle shape for forming a magnetic path; and a pole 5b formed integrally with the yoke 5a as a circular arc shape at both sides of an inner circumference surface of the yoke 5a. 
A neck portion of the winding groove 5c is provided in order to reduce an amount of the coil 6, and an edge of the winding groove 5c is formed as a curved line in order to prevent coating of the coil 6 from falling off when the coil 6 is wound.
Also, an insulator 7 for insulating the coil 6 from the pole 5b is attached to an outer side of the pole 5b and the winding groove 5c and an inner side of the yoke 5a which are contacted with the coil 6.
However, the powder metallurgy method has a disadvantage that a magnetic permeability of magnetic powder and core loss characteristic are lower than silicon steel used in the lamination method and material cost is expensive.
Herein, the magnetic permeability is called as magnetic inductive capacity, which means a ratio between magnetic flux density generated at the time of magnetization by magnetic field and intensity of the magnetic field in a vacuum state.
Also, the core loss characteristic means loss generated by steel in a unit volume, and silicon steel has more excellent core loss characteristic than iron powder. That is, since the silicon steel has more excellent magnetic flux density than the iron powder, the motor efficiency is relatively better.
In the powder metallurgy method, the frame is formed by using the mold thus to have an easy fabricating process, the winding groove is formed at the neck portion of the pole thus to reduce consumption amount of the coil, and the curved line is formed at the winding groove thus to prevent the coil from falling off at the time of being wound. However, cost of the magnetic powder is considerably expensive than the silicon steel.
Also, since the magnetic powder has low permeability and the core loss characteristic than the silicon steel, a frame of a larger volume is required in order to obtain the same effect with a motor using the conventional silicon steel, thereby increasing material cost.